1. Field of the Invention
The present invention relates to duckbill valves utilized to control the direction of fluid flow, and, more particularly, to a new duckbill valve that is normally biased to a closed position.
2. Description of Prior Art
Duckbill valves are widely utilized in a variety of applications to prevent the reversal of the direction of flow of various fluids and fluid combinations including liquids, gases, and aerosols. Though simple and inexpensive to manufacture and use, conventional duckbill valves are not without problems.
A typical prior art duckbill valve is illustrated in FIGS. 6, 7, and 8. Valve 50 comprises a body member 52 provided with an axial fluid passageway 54. Body member 52 smoothly tapers from an inlet end 56 to form a wedge-shaped outlet end 58 having an outlet slit 59 defining a pair of resilient sealing lips 60 and 62. As shown in FIG. 8, lips 60, 62 are of a uniform width throughout their respective lengths.
Body member 52 is usually formed of a resilient elastomeric material which is molded into the configuration shown in FIGS. 6-8. This forming process results in a slight amount of heat induced shrinkage to the resilient material of the valve body which imparts a slight opening bias along the length of lips 60, 62, normally urging the lips to a slightly open position.
In operation, valve 50 is usually sealingly positioned in line with a fluid conducting conduit (not shown). A flow of pressurized fluid, as symbolized by the arrow 36, is directed along the conduit and into inlet end 56 of valve 50, along axial passage 54 to outlet end 58 where the pressure exerted by the fluid flow between the adjacent sealing lips deforms lips 60, 62 further away from one another to open outlet slit 59 of the valve to permit fluid flow therethrough. If fluid flow stops or reverses direction, the resilient lips are intended to resume their normal shape and position and the back-pressure exerted by the fluid upon the outer surfaces of the sealing lips forces lips 60, 62 into sealing engagement against one another, closing outlet slit 59 and preventing the backflow of fluid through the valve.
However, in such prior art duckbill valves, a sufficiently strong backflow of fluid quite often will collapse or distort body member 52 causing lips 60, 62 to distort open and leak a reverse fluid flow as a result. Additionally, prior art duckbill valves such as that of FIGS. 6-8 tend to remain open under no flow or low flow conditions, the resiliency of the sealing lips being of insufficient strength to overcome the slight opening bias and to displace the static fluid between the lips to close the valve and prevent fluid leakage.
Early attempts at preventing this undesirable valve body member distortion and resultant fluid leakage are exemplified by U.S. Pat. No. 2,328,382 (Longden), issued Aug. 31, 1943, and U.S. Pat. No. 2,642,259 (Catlin), issued June 16, 1953. Both patents teach the insertion of a rigid cage or spider member within the axial passageway of the valve body member to maintain the shape of the valve body under backflow conditions. While sometimes successful at reducing valve body distortion and leakage, these rigid inserts add to the complexity and expense of the valve and restrict fluid flow through the axial passageway of the valve.
Accordingly, it is a principal object of the present invention to provide a duckbill valve that will be selfbiased to a normally closed position.
It is an additional object of the present invention to provide a duckbill valve that will resist deformation and collapsing.
It is a further object of the present invention to provide a unitary duckbill valve that will be biased to a normally closed position and that is configured so as to resist opening in the desired direction.